Sea Navigation Radar
Sea Navigation Radar
Sea Navigation Radar
Table of Contents
1-3) 3-5) Principles of Radar Radar System Configurations 5-6) Radar Terminology 6-8) 9) Radar Controls Targeting Birds
10-11) Range, Bearing and Position 12-14) Advanced Radar Operation 15-18) Radar FAQ's 19) 20) 21) Additional Resources Radar Mark Definitions Maintenance
When it comes to safety on the water, no other piece of electronic equipment on your bridge is as important as your Radar. For more than 30 years, Furuno Radars have consistently won the prestigious NMEA (National Marine Electronics Association) award for Best Radar. Whether you are looking for a compact 2.2kW unit or a commercial grade 50kW Radar, Furuno is the single largest source of Radars you can rely on. This book will help you learn about what a Radar is, how it works, and how to get the most from what is perhaps the most important navigation device you will ever own.
Boats of all types can benefit from having a Radar onboard for navigation and situational awareness..
1. Principles of Radar
What is Radar?
Radar is an acronym meaning RAdio Detecting And Ranging. It is a device which measures not only the time it takes for a pulsed signal to be reflected back from an object but also its bearing relative to your position. No other piece of marine electronics can give you as much information about objects around your own ship as Radar.
Collision avoidance
The guard alarm feature of every Furuno Radar alerts you when targets enter a particular area, or own ship is nearing a danger area. The alarm area can be forward of own ship or a 360-degree circle around the vessel. When Radar targets such as other ships, landmasses or buoys enter the zone, an audible alarm sounds to alert the operator.
D = 1/2 x cT c = Speed of Radio Pulse (3 x 108 m/sec) T = Time between transmission of radio pulse and reception of reflected echo D = Distance Both radio waves and light travel at the near-constant speed of 186,000 miles per second; therefore, the Radar can process vast amounts of information in a very short time. Comparatively, Sonar and Fish Finders use ultrasonic waves rather than radio waves. Since the propagation speed of the ultrasonic wave is 1,500 miles per second, signal processing is much slower with these devices than with Radar.
Fishing operation
Besides its basic function as an aid to navigation, Radar is also a valuable tool for fishing operations. Purse seiners use it to monitor net shape, observing the echoes from floats attached to the net. It is especially useful in fleet fishing for determining position of vessels, locating fishing grounds and positioning vessels. Specialty fisherman use Radar to search for sea birds, which may be an indication of the presence of bait fish or their target species. This technique has become easier with the advent of dual-range simultaneous scanning, such as that found in NavNet 3D, where the navigator can use one Radar screen with the gain set for targeting birds, while the other Radar screen is used to navigate. As you can see, for many fishing vessels Radar functions more often as an aid to fishing rather than an aid to navigation.
How It Works
Did you ever shout at a cliff and hear the echo of your shout? Radar works in a similar manner. Imagine that radio pulses are emitted from the scanner in a certain direction. When the pulse strikes an object such as a ship or island some of the energy returns to the scanner. The direction in which the scanner is pointing when the reflection is received is the direction of the target causing the reflection. Since radio waves travel at a near-constant speed, the time required for the reflected echo to return to the scanner is a measure of the range to the target.
Almost all late model Radars use Liquid Crystal Display (LCD) or daylight bright Cathode Ray Tube (CRT) displays. These types of displays provide steady, bright, non-fading Radar echoes in monochrome or color depending on model. The picture is visible even in full daylight. Digital information is displayed on-screen to keep you informed of your navigational situation at all times.
Radar range
Atmospheric conditions and target shape, material and aspect slightly affect Radar range. However, Radar range is generally calculated as follows:
Figure 1 - Determining Radar range D is the distance from the scanner to the target horizon. Under normal atmospheric conditions, this distance is 6% greater than the optical horizon. This is because radio waves bend or refract slightly by atmospheric change. The higher the scanner or target is above the surface, the longer the detection range. For example, if the scanner is 9 meters above the sea surface and the height of the target is 16 meters, you should be able to see the targets echo on the display when the target is 15 miles from the Radar.
Magnetron
The magnetron generates the radio pulses. Magnetrons, as well as the Radar itself, are classified by their transmitting frequency band. There are two main frequency bands in commercial Radar: X-Band (9,000 MHz band; wavelength 3cm) and S-Band (3,000 MHz band; wavelength 10 cm). Magnetron output power ranges from 1kW for small Radars to 60kW for large Radars. Table 1 compares the S-Band and X-Band frequencies.
Table 1 - Comparison of X-Band and S-Band Frequency Band Characteristics Short wavelength for better X-Band directivity Attenuation in precipitation is greater than on S-Band Small, light-weight antennas Longer wavelength for long S-Band range detection Penetrates precipitation for excellent performance in inclement weather Large antenna
The length of the array affects horizontal beamwidth, and thus the Radars ability to determine target bearing. The longer the array, the more accurately the Radar can determine bearing. For example, an array of 50 cm length gives a horizontal beamwidth of 5 degrees, while one of 300 cm length gives a horizontal beamwidth of 0.75 degrees. Scanner directivity is a measure of the two beamwidths. One is in the horizontal plane, known as horizontal beamwidth, and the other is in the vertical plane, known as vertical beamwidth. The narrower the horizontal beamwidth the sharper the beam. The vertical beamwidth should be wide; it is typically 20 to 25 degrees. The main reason for a wide vertical beamwidth is to ensure the ability to display a target while own ship is pitching and rolling.
Modulator
The device responsible for monitoring the magnetron for proper operation is the modulator. It ensures that the magnetron transmits at exactly the same frequency throughout the duration of the pulse, and that the time between pulses is the proper length.
Limiter
The limiter protects the receiver circuits from damage in the event own ships Radar receives radio pulses from another ships Radar. When this occurs, the limiter attenuates them to protect the next stage MIC (Microwave Integrated Circuit).
TX/RX Switching
A TX/RX switching device enables the Radar to transmit the radio pulse and receive its reflected echo through one scanner. The switching device used by the Radar is called a circulator It consists of a permanent magnet and a ferrite core. When transmitting, it directs radio pulses to the scanner and disconnects the receiver circuits. When receiving, it funnels weak reflected echoes away from the magnetron to prevent both flow to the magnetron and loss of receive signal.
MIC
MIC is an acronym meaning Microwave Integrated Circuit. The MIC consists of a local oscillator and mixer circuits. Incorporating those devices on an IC improves quality, reliability, sensitivity and noise figure (nf).
Scanner
The scanner transmits the radio pulses and receives their reflected echoes. Most scanners rotate at a constant speed of 24 rpm. Many modern Furuno Radar scanners rotate at variable speeds dependent upon the range in use in order to optimize Radar detection. The type of scanner used by most vessels is the slotted array, an antenna with a series of slits spaced at suitable intervals and angles from which radio pulses are transmitted. The reflected echoes also pass through these slits. Figure 4 - A typical slotted array scanner
IF Amplifier
The IF amplifier amplifies the Intermediate Frequency signal output by the MIC.
A/D Converter
The received IF signal is an analog signal. This signal is converted to a digital signal in order to undergo various processing in the display unit. The A/D (Analog to Digital) converter converts analog signals to digital signals.
Range resolution is a measure of the capability of the Radar to display as separate pips the echoes received from two targets that are on the same bearing and are close together. The main factor that affects range resolution is pulselength. A short pulselength gives better range resolution than a long pulselength.
Signal Processing
This section is the heart of the Radar and contains computers, memories, and other ICs. Extensive use of digital techniques permits high speed processing.
Control Unit
The control unit contains various keys and controls for adjustment of the Radar picture. Whenever a control setting is changed the associated reaction appears almost immediately on the display. In some Radar designs, the control unit is separate from the display unit.
Figure 7 - Example of range resolution Generally, use a short pulselength on short ranges for better range resolution, and a long pulselength on long ranges for longer range detection.
Control Description:
Power: Powers the entire Radar system. After
turning on the power, a timer displays the time remaining for transmission preparation. ST-BY appears when the Radar is ready to transmit. The method of turning off the power varies by model; consult your Operators Manual for details on powering off your Radar.
Maximum detectable range and output power: Doubling the output power of a typical
Radar raises the maximum detectable range by only 19 percent. In the reverse case, halving the output power lowers the maximum detectable range by 16 percent. While you can increase the maximum detectable range by using a high output power Radar, a better (and more economical) way to do it would be to mount the scanner as high as possible above the waterline and/or utilize a longer antenna to increase horizontal beamwidth.
2. RADAR CONTROLS
This section briefly describes the function, objective and usage of Radar controls. Note that some controls described here may not be provided on your Radar. For detailed control description, refer to your Operators Manual.
Precautions:
A rotating scanner is dangerous. Before turning the Radar on, be sure no one is near the scanner unit. The scanner unit emits high frequency radio pulses, which can be harmful, particularly to your eyes. Never look directly into the scanner unit when the Radar is in operation.
Key response: The Radar normally releases a beep when you correctly enter a command. If no beep is released, try again. Incorrect command generates several beeps. This function can usually be disabled, but caution must be used as this audible feedback is important to verify correct entry of commands.
Echo Trails: This feature continuously shows the movements of other ships in afterglow. It is useful for assessing target movement and collision possibility. Display Mode: The display mode determines target
position and movement on the display. There are two types of display mode: Relative and True. Relative Bearing Display: This mode is also known as Head-up, since own ships heading is always at the top of the display. The position of own ship is fixed and echoes of all other objects therefore move relative to own ship. This is the usual form in small Radar sets. True Bearing Display: This mode is sometimes called North-up since the display is oriented North. This mode is suitable for long -range observation since it is somewhat like looking at a nautical chart.
Brill: This control adjusts the display brilliance. Range: Press the [+] and [-] keys to raise and lower the range respectively. When you change ranges, the number of range rings and range ring interval as well as pulselength are automatically changed. For confirmation, the range and range ring interval appear on the display. Rings: Press this key to show or hide the range
rings. Range rings provide an estimate of the range to a target. The number of range rings and range ring interval automatically change with the range. Ring interval (distance between rings) appears on the display.
Index Lines: Index lines are useful for maintaining a constant distance between own ship and the coastline or a partner ship. Press the key to toggle index lines on and off.
HM Off: The heading mark may sometimes hide a small echo. To show that echo, press and hold down the HM OFF key to temporarily erase the heading mark . Release the key to display the heading mark. Echo Stretch: This function stretches small
echoes to make them easier to see. It stretches not only small echoes but also returns from sea and rain clutter and Radar interference. For this reason, make sure clutter and interference are sufficiently suppressed before using echo stretch.
Echo Averaging: The Radars internal circuitry processes echo data to obtain a desired effect. The result depends on the Radar model. For example, some Radars may suppress brilliance of unstable echoes (sea clutter, etc.), or emphasize an unstable small echo. Huer, Color, Background Color: These
settings change display color and background color respectively to improve display visibility. Note that marks and characters also change color when the keys are pressed.
Figure 9 shows a sample Radar display. Own ships position is at the display center. The Radar range is 12 nautical miles and the range ring interval is 2 nautical miles. The circled objects are ARPA targets and the triangle objects are AIS targets. The large, continuous echoes are from land masses. Note that the actual shape of a target cannot be displayed on the Radar - only the portions struck by the radio pulse appear on the display.
When operating in Head Up or True Motion, be sure to turn on your target trail These birds were targeted using the Furuno 1954C function and set NavNet Radar. True Color is highly desirable when it for long trails targeting birds, as demonstrated above; these flocks were to help track easily picked out in red against the blanket of clutter. travelling flocks. for maximum sensitivity in order to detect birds. Resist the temptation to turn up the AC/Sea or AC/Rain to drop out the noise. Flocks of birds may look like dense, recurring noise rather than a solid target, but you Practice these techniques and soon you will be scouting your fishing spots just like the pros.
UHD offers crystal clear, noise-free target presentation with automatic real-time digital signal processing. Antenna rotation speed (24/36/48 rpm) is automatically shifted to the appropriate pulse length.
By EBL:
Display an EBL and adjust it so that it bisects the target. The bearing to the target appears on the EBL readout. Bearing relative to heading is relative bearing, while bearing relative to North is true bearing.
Measuring Range
The range from own ship to target can be measured in three ways: by range rings, by cursor, and by VRM.
By Range Rings:
The RINGS key shows/hides the range rings and adjusts their brilliance. To measure range by the range rings, count the number of rings between the center of the display and the echo. Check the range ring interval at the top of the display and judge the distance of the echo from the inner edge of the nearest ring.
By Cursor:
The cursor provides a more accurate measurement of range You can determine true bearing by adding relative to targets. Set the cursor intersection on the inner edge of bearing to your compass reading. If the sum is over the target. The range from own ship to target appears on the 360 degrees, subtract 360 from the number. display.
No Gyrocompass Connection:
By VRM:
The VRM, like the cursor, provides a more accurate measurement of the range to targets. Display a VRM and adjust it so that it rests on the inner edge of the target. The range to target appears on the VRM readout.
Gyrocompass connection:
Select the true bearing display, north-up mode. Measure the bearing by the EBL and check the EBL readout.
Measuring Bearing
The relative bearing from own ship to targets can be measured by the cursor and by the EBL. With gyrocompass connection, you can display true bearing.
AIS provides real-time informat AIS-ready chart plotter, navigation presented graphically, allowing you t sels in the area. Since AIS targets can b line of sight, the system greatly enhance waterways, limited visibility or heavy sea co more information about AIS equipped vessels.
By Cursor:
Set the cursor intersection on the center of the echo. The bearing from own ship to target appears on the display.
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General Procedure:
Turn the A/C SEA control fully counterclockwise (down). Turn the GAIN control fully clockwise (up). Slowly turn the GAIN control counterclockwise (down) to reduce sea clutter and distinguish targets. Note that echoes that are weaker than the sea clutter will not appear. If this action does not remove sea clutter near own ship, gradually turn the A/C SEA control clockwise (up) to reduce sea clutter. NOTE: The A/C RAIN control is also effective in suppressing sea clutter. It is most effective when the echo of the target is larger than that of the sea clutter. Its main advantage over the A/C SEA control is that, when used to suppress sea clutter, it does not shrink small echoes.
An ARPA target is measured by range and bearing from own ship and located on the Radar PPI. When ARPA and AIS are combined and their symbols are within an operator-set criteria, the ARPA symbol is merged with the AIS symbol. Some common ARPA symbols are:
tion about AIS-equipped vessels on your n software or Radar. This information is to monitor and avoid AIS equipped vesbe received even if they are not within es situational awareness in congested onditions, and gives the navigator much Some common AIS symbols are:
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Precipitation
Rain, snow and hail may return echoes which appear on the display as a blurred or cluttered area. You can suppress them by adjusting the A/C RAIN control, or lowering the sensitivity.
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False Echoes
Occasionally false echoes appear on the screen at positions where there is no target. In some cases the effects can be reduced or eliminated. The operator should become familiar with the appearance of these false echoes so as not to confuse them with echoes from legitimate contacts.
Indirect echoes
Indirect echoes may be returned from either a passing ship or from a reflecting surface on your own ship, such as a stack. Figure 12 illustrates the effects of an indirect echo. Indirect echoes may be recognized as follows: They usually occur in shadow sectors They appear on the bearing of the obstruction but at the range of the legitimate contact When plotted, their movements are usually abnormal Their shapes may indicate that they are not direct echoes
RACON
The RACON (RAdar beaCON) automatically transmits a signal when it receives a radio pulse. The signal transmitted by the RACON appears intermittently on the display as a Morse character, a dashed or dotted line radiating out from the beacon. In the U.S., RACONs are used to mark lighthouses and buoys, inconspicuous coastlines, navigable spans under bridges, offshore structures such as oil platforms, or environmentally sensitive areas such as coral reefs.
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Multiple Echoes
Multiple echoes can occur when a strong, short-range echo is received from a target. A second, third or more target may be observed on the display at double, triple or other of the actual range of the target. Multiple reflection echoes may be reduced or often eliminated by decreasing the sensitivity.
Radar Interference
Radar Interference occurs when in the vicinity of another Radar operating on the same frequency band, normally 9GHz; 3GHz for large Radars. It is usually seen on the display as large numbers of bright dots either scattered at random or in the form of dotted lines extending from the center to the edge of the display. The interference effects are easily distinguishable from normal echoes because they do not appear at the same places on successive rotations of the scanner. You can reduce the interference effects by turning on the interference rejection.
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Radar FAQ's
We've gathered a list of some of the most frequently asked questions about Radars and provided the answers in this section. If you have a question that is not answered in this book, you can visit us on the web at www.FurunoUSA.com and click on the Support button. You can browse through answers to questions, or search for your answer by model, topic or keyword. If you can't find the answer you're looking for, you can send an E-mail directly from our web site to our technical support staff. A knowledgeable technician will respond with your answer, generally within 48 hours.
Q: How do I adjust my new Furuno Radar for the best presentation? A: Normally the auto features will work well for most situations. If you want to adjust the Radar manually try the following: 1) Transmit the Radar in maximum range 2) Set STC (sea clutter) to minimum 3) Set FTC (rain clutter) to minimum 4) Set the gain control to maximum (the screen should show mostly Radar noise) 5) Now adjust the gain control to show a very small amount of noise (only a few noise spots on the screen) 6) Without disturbing the gain control select the appropriate working range 7) Adjust STC(sea clutter) as desired 8) Adjust FTC(rain clutter) if needed Note: The timing and heading must still be set according to the procedure listed in the installation manual. Q: Should I manually tune my Furuno Radar or use the automatic tuning feature? A: Unless a problem is suspected with the automatic tuning circuit, automatic tuning is superior to manual tuning. The automatic tuning circuits adjust the receiver sensitivity to each transmitted pulse. It would be impossible to duplicate this procedure using manual tuning. Most Furuno Radars have an automatic tune compensation adjustment that must be done as part of the initial installation alignments. See installation manual for more information on initial set-up. Q: My Radar is showing targets in the wrong place (i.e. the buoy in front of the boat is showing on the Radar as a target behind the boat). My compass heading input is correct and the Radar is in head-up mode. How do I correct this? A: All Radars require a heading alignment upon installation of the Radar antenna. Refer to your installation manual for the proper procedure in completing this adjustment. Once you complete the heading alignment the targets should show in the correct places. Q: My Radar turns on but will not go into transmit. It has a message on the screen that says HD/BP, what does that mean? A: The error message HD/BP indicates that the display is not getting heading or bearing pulse signals. The first step is to see if the antenna is turning. If you have an open array this is easy to check, but if you have a radome antenna you will need to remove the cover to check for rotation. You will need to contact an Authorized Furuno representative. This information will help them start the troubleshooting process. Q: How does UHD Radar work? A: Furunos Ultra High Definition Radars use a new digital processing technique that effectively doubles the scan lines on the screen, dramatically improving resolution. Additionally, vastly improved Auto Modes employ digital filtering and modeling techniques that allow the Radar to adapt to a variety of sea states.
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Additional Resources
www.FurunoUSA.com:
Visit our web site at www.FurunoUSA.com for information on the entire line of award-winning Furuno Radars. Browse through our catalog of chart plotters, fish finders, sonar, communication products and PC software to round out your helm.
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Mark Display:
Table 2 describes the marks commonly found on Furuno Radars. Mark Cursor Tuning Bar Heading Mark Appearance Description
The cursor is controlled by operating the trackball, arrow keys or omnipad. Its main function is to measure range and bearing to a target, select AIS and ARPA targets, and set guard zones The tuning bar shows receiver tuning state. Normally, a longer bar indicates better tuning, however the length of the bar can vary with range and number of targets. The heading mark shows own ships heading. With no gyro or fluxgate compass the mark always points to zero degrees. This mark appears when a gyro or fluxgate compass is connected to the Radar. The short dashed line always points to north. Range rings provide an estimate of range to target. The interval and number of rings may change with range. Variable Range Marker. These marks appear on the display as dashed circles. The length of the dash of the #2 VRM is longer than that of the #1 VRM. They function to measure range to target. Electronic Bearing Line. These marks appear on the display as dashed lines. The length of the dash on the #2 EBL is longer than that of the #1 EBL. They function to measure bearing to target. The guard zone defines an area which, when targets enter or leave as per user settings, an audible alarm is triggered to alert the user to the change.
+ +
+ + +
North Mark
Range Rings
VRM
+ + +
EBL
Guard Zone
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4. MAINTENANCE
Regular maintenance is important for continued performance of the Radar. Before reviewing this section, please read the safety information which follows.
6 Months Check the scanner drive motor brushes. The life of these carbon brushes is about 2,000 to 1 Year hours. If their lengths are less than 6 mm, replace them with new brushes, which are 11 mm
long. Carbon dust given off by the scanner drive motor brushes may fall into the slits of the timing disk. This may cause the sweep on the display to jump. Check the slits for carbon dust and foreign material.
1 Year
Check that all wiring on terminal boards is secure. Check that all plugs and jacks are properly seated.
Table 3 above outlines a suggested regimen of maintenance that you may follow to get the best performance from your Radar. Preventive maintenance greatly extends the life of the equipment. A maintenance program should be established and should at least include the items listed above.
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